The invention relates to a screw mill for comminuting and compressing a material used for grinding. A screw mill of the type under discussion comprises two motor-driven conveyor screws or screw conveyors mounted in rotary, juxtaposed manner in a casing. A charging opening is provided in the casing crest on the inlet side and a shaping and compressing head is positioned in the casing end on the outlet side.
Screw mills for comminuting and compressing grinding material are known in various different constructions. A rough distinction is provided by the number of conveyor screws used, i.e. one, two or more screws. A further distinction is possible as to whether additional means are used in the form of nozzles and orifice plates in order to bring about an additional grinding and compressing.
In a known screw press of this type disclosed in EP 108763, the casing comprises casing elements, in which are mounted two conveyor screws formed from screw elements. Between the casing elements, are arranged orifice plates, which block the passage of the conveyor screws with the exception of a relatively small constriction or throttle gap. The conveyor screws are driven by means of a gear and the shafts of said screws extend through the gear and are supported on a journal bearing, which is fixed to the casing by means of draw rods.
The purpose of the known screw press is that it can be used, without significant reconstruction, for processing widely differing materials. The pressed out liquid is sucked off and the solid can be dried and briquetted by a shaping head. Although the use of orifice plates makes it possible to open up the grinding material, particularly organic material, due to the movement on the orifice plate, i.e. the cell walls are opened, considerable wear takes place on the orifice plates and even when the coating is of hard metal, a considerable amount of wear still occurs. The further disadvantage is that the use of orifice plates or similar constricting members leads to a reduction in the processing capacity.